MICHIGAN, ARIZONA (CBS News) -- After all the votes are counted, Mitt Romney will have won the Arizona and Michigan primaries, CBS News projects. Votes are still being counted in both states.
While Romney has long held the lead in Arizona, the race in Michigan was unexpectedly competitive and one of the closest of the GOP campaign so far. Though Romney was born in Michigan and his father was a governor and top auto executive there, Santorum surged ahead of his rival in early February as voters connected to the social conservative. Romney regained his footing in recent days and polls showed the two candidates in a statistical dead heat going into Tuesday's contest.
In Arizona, with 1,810 of 2,181 precincts reporting, Romney has 47 percent of the vote. Santorum has 26 percent while Newt Gingrich has 16 percent and Ron Paul has 8 percent.
With 5,129 of 5,233 precincts reporting in Michigan, Romney has 41 percent of the vote. Santorum has 38 percent while Paul has 12 percent and Gingrich has 7 percent.
"We didn't win by a lot, but we won by enough, and that's all that counts," Romney said in Novi, Michigan Tuesday night, before diving into an attack against President Obama.
While the number of delegates at stake are roughly the same for both states, Michigan was more closely watched because the second place finisher will garner some of the delegates, and the results have been cast as a referendum on Romney's candidacy.
With Gingrich essentially ceding the state and Paul trailing there, the Michigan primary was seen as a test as to whether Republican primary voters preferred a polished, diligent candidate like Romney or a passionate populist like Santorum.
CBS News early exit polling showed that Arizona and Michigan primary voters were primarily concerned with picking a candidate that can defeat President Obama. Among the issues they care about, voters said the economy is the most important.
When it comes to electability and handling the economy, exit polling showed Michigan voters have the most faith in Romney. Among those voters primarily concerned with defeating Mr. Obama, 61 percent backed Romney, while just 24 percent voted for Santorum. Eight percent voted for Gingrich, and 4 percent voted for Paul.
Among Michigan voters who picked the economy as their top issue, 47 percent backed Romney, while 30 percent supported Santorum.
Among Arizona voters who picked the economy as their top issue, 51 percent backed Romney, exit polling showed, while 26 percent backed Santorum. Romney is seen as most electable in Arizona.
In his remarks Tuesday night, Romney focused on the economy and attacking Mr. Obama's job performance: "Four years ago we warned that the presidency was no place for on-the-job training," he said. "Well, today we have the economy to prove it."
With Tuesday's victory in Michigan, Romney dodged an embarrassing loss on his home turf. A win also gives the former Massachusetts governor some crucial momentum ahead of Super Tuesday on March 6, when 10 states will weigh in and a whopping 437 delegates will be decided.
But even though Romney pulled ahead of Santorum in Michigan, the hard-fought race underscored Romney's weaknesses. He has been incapable so far of winning robust support from his own party in spite of his well-organized campaign efforts.
Santorum's performance against his better-funded rival was impressive, and Tuesday night, he cast the results in a positive light. "A month ago, they didn't know who we are, but they do now," he told his cheering supporters.
The former senator attempted to appeal to a group of voters once referred to as "Reagan Democrats" -- working class, social conservatives -- with a mix of economic populism and social values. In spite of his losses Tuesday night, Santorum could still perform well on Super Tuesday, when three southern states vote (Tennessee, Oklahoma and Georgia), as well as Ohio, where polls show Santorum in the lead. However, Santorum is likely to be hounded still by questions of whether his campaign can appeal to more than just the conservative base.
CBS News exit polling in Michigan showed that working class voters -- the voting bloc Santorum has been chasing -- nearly split between the leading candidates. Santorum had a slight edge among voters making less than $50,000 a year, garnering 41 percent to Romney's 36 percent. Among voters without a college degree, Santorum won 39 percent while Romney won 37 percent.
Though Romney has regained his footing somewhat, the race could go on for a number of months. A candidate needs 1,144 delegates to secure the nomination; even after the Michigan and Arizona delegates are allocated, the candidates will still be far from what they need for victory.
Michigan's 30 delegates will be awarded proportionally, which benefits Ron Paul, who has focused on accumulating delegates if not winning states outright.
After Tuesday night's primaries, Romney leads in CBS News' Delegates to Date Estimate, with 157 delegates. Santorum has 52, while Gingrich has 30 and Paul has 15.